1. Field of the Invention:
The invention relates to polymer blends, in particular polymer blends of aromatic polycarbonate and methacrylate polymers or copolymers.
2. Discussion of the Background:
Polymer blends containing an aromatic polycarbonate as one component and a vinyl polymer as another component are known. According to German Patent Publication 23 29 585, pages 11 to 12, completely homogenous and transparent polycarbonate molding composition blends are obtained when an aromatic polycarbonate of 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, which is an o,o,o',o'-tetraalkylated bisphenol, is mixed, for example, with polystryene as a thermoplastic resin.
In contract to this, according to this German Patent Publication, a mixture of 2,2-bis(4-hydroxyphenyl)-propane polycarbonate, which is the polycarbonate of Bisphenol A, and polystyrene, comprises two phases. Other thermoplastic resins that behave like polystyrene in these mixtures, as described in the German Patent Publication at pages 5 and 6, are homopolymers and copolymers of acrylic and methacrylic compounds such as, for example, methyl acrylate, ethyl acrylate, methyl methacrylate, and cyclohexyl methacrylate.
Polymethyl methacrylate, a glass-clear, transparent plastic, with the polycarbonate of Bisphenol A, a likewise transparent plastic, does not give homogenous transparent alloys. As disclosed among other features in Japanese Patent Publication 72 16 063, these mixtures have an opalescent luster.
According to German Patent Publication 22 64 268, an improved polycarbonate molding composition is obtained when a low molecular weight acrylic polymer which is a copolymer consisting of 90 to 75 wt. % methyl methacrylate and 10 to 25 wt. % of an alkyl acrylate with the formula CH.sub.2 .dbd.C(X)--COOR, with X being H or CH.sub.3 and R being an organic group with 4 to 12 carbon atoms, is added to the polycarbonate. The amount of copolymer additive can be 0.01 to approximately 50 wt. % of the weight of the polycarbonate composition. Increasing addition of copolymer steadily reduces the melt viscosity of the polycarbonate or of the mixture without impairing the transparency.
These copolymers are therefore polymeric plasticizers whose molecular weight to produce the described compatibility, based on our own experiments with appropriate copolymers, has to be below 15,000. However, such copolymers are completely unsuitable for producing polymer alloys that also have industrially interesting properties in the range of high polymethacrylate fractions, because of the known decline in mechanical properties in the molecular weight range below 100,00, especially below 50,000 (see Plastics Manual, Volume IX, Vieweg/Esser: Polymethacrylates, pages 112 ff).
Compatible polymer blends that consist of a polycarbonate such as bisphenol A polycarbonate and a copolymer of monomeric esters of acrylic and/or methacrylic acid with C.sub.1 -C.sub.10 alcohols and a UV-absorbing monomer of the formula ##STR1## in which R.sub.1 stands for hydrogen or a methyl group and Y stands for oxygen or an NR.sub.2 group with R.sub.2 being a hydrogen or an alkyl group and Z being a UV-absorbing group, namely a 2-hydroxyphenyl-benzotriazole group a 2-hydroxybenzophenone or acetophenone group, or an .alpha.-cyano-.beta.,.beta.-diphenyl group, are described in German Application P 35 18 538.4.
Such polymer blends of polycarbonate and copolymers of methyl methacrylate and monomers with pronounced absorption power for ultraviolet radiation, which can also be processed as thermoplastics and which are used as optical screening agents to improve the light resistance of plastics, for example, especially by coating them, are polymer blends with only special uses. Because of the high cost of the UV absorbers compounded with them, these blends are prohibitively expensive and cannot be used as widely usable, thermoplastically processable compositions.
Thermoplastically processable methyl methacrylate copolymers with methacrylamides as comonomers that are substituted on the amide nitrogen with an organic group of a cyclic molecule, which also have no distinct UV absorption power, are described in German Application P 36 32 946.0. These copolymers form transparent, thermoplastically processable polymer blends with polycarbonates, especially Bisphenol A polycarbonates.
Thermoplastic molding compositions as polymer blends of a polycarbonate, a copolymer of styrene, methyl methacrylate, and N-phenylmaleimide, and a graft polymer of methyl methacrylate on rubber, are not compatible, according to European Patent Publication 173 146. In the same way, the polymer blends disclosed by European Patent Publication 144 231 made up of a polycarbonate and a copolymer of methyl methacrylate/N-phenylmaleimide and/or an EPDM-g-methyl methacrylate/N-phenylmaleimide copolymer, are not fully compatible.
Transparent, thermoplastically processable polymer blends of aromatic polycarbonates, especially the polycarbonate of Bisphenol A, and a methacrylate copolymer that is made up of methyl methacrylate units and N-cyclohexylmaleimide units, are described in German Application P 37 09 562.5. Other additional monomers can also optionally be used to construct the methacrylate copolymer, in amounts of 0 to 40 wt. %, such as cycloalkyl or alkyl esters of acrylic or methacrylic acid, among others. The polymer blends, like those from 0 36 32 946.0, in comparison with the individual components, namely Bisphenol A polycarbonate or polymethyl methacrylate, can be used beneficially as optical resin materials because of their low optical birefringence and/or reduced water uptake.
Polymer blends of aromatic polycarbonate and methyl methacrylate copolymers with comonomer building blocks containing nitrogen also show properties that detract in particular from their use as optical resin materials. It has long been known of polymer materials containing nitrogen that changes occur during their thermoplastic processing, especially in the presence of O.sub.2, with the extruded or injection molded parts obtaining a discolored yellow color.
The problem therefore exists of finding transparent, thermoplastically processable polymer blends made up of aromatic polycarbonate and a polymer that is made up of methyl methacrylate in high proportions, with the methyl methacrylate polymer being modified by the incorporation of other monomers so that it becomes compatible with the polycarbonate. The new blends prepared in this way would no longer have the deleterious properties that have appeared heretofore.